Docker/C2/Building-Docker-Images/English
| Visual Cue | Narration |
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Welcome |
Hello and welcome to the Spoken Tutorial on “Building Docker Images”. |
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Learning Objectives |
In this tutorial, we will learn about
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System Requirements |
To record this tutorial, I am using
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Code files |
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| Show Slide: | These are the steps for building Docker images.
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Building Docker Image Process Flowchart |
In this tutorial, we'll build an Express web server using a custom Docker image.
This flowchart explains the process of building a Docker image. |
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Hover over Dockerfile block |
To build a Docker image, we need a Dockerfile which is a text document. |
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Building Docker Image Process Flowchart |
The folder express underscore api contains app dot js file for the application. |
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Building Docker Image Process Flowchart |
The image will be built using docker build command. |
| The image will run the application code.
We need a nodejs environment for running the Express web server. | |
| We will use the official Node js image from Docker Hub as the base image. | |
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Building Docker Image Process Flowchart |
After the image is built, docker run command is used to run the image.
A new container will be created based on the image. It will execute the commands and run the Express server on our Linux OS. |
| Only narration | Let us see how to implement this. |
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Point to Downloads folder |
I have downloaded the code files and saved it in my Downloads folder. |
| Open Downloads directory in file manager. | We can see Dockerfile and express underscore api folder.
Let us open the Dockerfile in the text editor. |
| Only narration | Here,we have a set of commands required to create an image. |
| Highlight FROM node:latest | This command will pull the latest official Nodejs image from Docker Hub.
This is the base image for the application. |
| Highlight RUN | Here, RUN keyword executes the command specified after it. |
| Highlight mkdir /home/app | This command creates an app directory in the image’s file system. |
| Highlight COPY ./express_api /home/app | COPY command copies the contents of the express api folder into the app directory. |
| Highlight WORKDIR /home/app | WORKDIR command makes app directory as our working directory |
| Highlight RUN npm init -y && npm install express --save | This command installs the required Node js packages for our application. |
| Highlight CMD [ "node", "app.js" ] | The CMD command runs the Node js application. |
| Only narration | Next let us look into the code of our application. |
| Switch to Downloads directory in File Manager
Open app.js |
In the express underscore api folder, open the app dot js file in a text editor. |
| Only narration. | This application uses the Express framework to create a web API. |
| Highlight const express = require('express'); | First we bring in the Express tool to help build the server using this command. |
| Highlight const app = express(); | Then, this command line creates the main app to handle requests and responses. |
| Highlight app.use(express.json()); | This command line allows the app to understand data sent in JSON format. |
| Highlight const PORT = 3000; | This command line set the port number to 3000.
The application will listen for incoming HTTP requests on this port. |
| Highlight app.get('/', async (req, res) => {
res.send("Express server is running"); }); |
When someone opens the main page, this command listens for their request.
It then sends back the message, Express server is running. |
| Highlight app.listen(PORT, () => {
console.log(`Server started at http://localhost:${PORT}`); }); |
app dot listen command displays the message in the terminal after the image runs.
It indicates that the server has started at the given site. |
| Only narration | Now let us build the image. |
| Open a terminal by pressing the keys Ctrl, Alt and T simultaneously. | Open a terminal. |
| Type cd ~/Downloads and press Enter | Change to the directory where you have downloaded the code files. |
| Type sudo docker build -t node-express:v1 . | To build the image, type the command as shown.
The flag hyphen t tags the image with a name. In this case, the image will be tagged as node hyphen express with version 1. If version is not specifically mentioned, latest will be given by default. The dot represents the path of the current directory. |
| Press Enter and enter the password when prompted | Press Enter. |
| Highlight the output | We can see that the building of the node hyphen express image is finished. |
| Type sudo docker images and press Enter | To show a list of images, type the command as shown and press Enter. |
| Highlight the node-express row | We can see our image, node hyphen express in the list.
Also, we can see details about its Tag, Image ID, creation date, and size. Tag identifies a specific version of the image. In this case, we have given it as v1. Our image is now successfully built. |
| Type sudo docker run -it --rm -p 3000:3000 node-express:v1 and press Enter | Now, let us run the image.
Type the command as shown. |
| Highlight -it | Hyphen it attaches an interactive terminal session. |
| Highlight --rm | hyphen hyphen rm flag automatically removes the container once it exits.
It helps in cleaning up resources. |
| Highlight -p 3000:3000 | This option maps port 3000 of the host to port 3000 of the container. |
| Only narration | Press Enter. |
| Highlight the output | We can see that the server has started. |
| Go to http://localhost:3000 | Open the browser and enter the given link. |
| Highlight Express server is running | The "Express server is running" message confirms the image is working. |
| Only narration | To stop the running image container, open a new terminal session.
You can do so by clicking on the plus symbol on the top panel of the terminal. |
| Type sudo docker ps and press Enter | Enter the command as shown.
Enter the password when prompted. This will retrieve the list of running containers. |
| Highlight node-express:v1 row | We can see the container of our image running.
Copy the container id. |
| Type sudo docker stop <Container_id> and press Enter | To stop the container, we will use docker stop command.
Type sudo space docker space stop space and paste the container id. Press Enter. |
| Highlight the output | We will get the container id of the stopped container as the output. |
| Only narration | Now let us see how to push the image to Docker Hub. |
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Pushing Images to Docker Hub |
To push a Docker image to Docker Hub, we use the push command.
Before pushing, we need to tag the image. It needs to be done with our Docker Hub username and the repository name. |
| Only narration | Let us see the execution of it. |
| Docker hub website :
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Go to the web browser, and enter the URL as shown.
Create your account by signing up. On the top left corner, click the list icon and choose the repositories section. The repositories section lists repositories, each containing Docker images. |
| Type sudo docker login and press Enter | Switch to the terminal.
Close the previous terminal session and use a new one. Type the command as shown. Using this command, we will log into our Docker Hub account. Then we can easily pull and push images to it. Press Enter Enter the credentials for Docker Hub when prompted. |
| Highlight Login Succeeded | We can see that our login has succeeded. |
| Type sudo docker tag node-express:v1 stuser1/node-express and press Enter | Before pushing, we need to tag the image with username.
To tag the image, enter the command as shown. This creates a reference to the image with the specified tag. Here, stuser1 is my username. Substitute it with your username. |
| Highlight stuser1/node-express | Stuser1 forward slash node hyphen express will be our repository name
It will be assigned after pushing the image to Docker Hub. |
| Type sudo docker push stuser1/node-express and press Enter | Next push the image to Docker Hub by typing the command as shown. |
| Highlight the output | This indicates that our tagged image is successfully pushed to Docker Hub. |
| Go to Docker Hub website and refresh the page. | Then we will go to Docker Hub website again and refresh the page. |
| Hover over stuser1/node-express | We can see our image in our repository indicating it is successfully pushed. |
| Only narration | Now let us tryto pull the image back from the repository.
For that, firstl et us delete the image from our local system. |
| Type sudo docker rmi stuser1/node-express and press Enter | To remove the image, we will use docker rmi command.
Enter the command as shown. |
| Highlight the output | We can see that the image is untagged, that is removed from the system. |
| Type sudo docker images and press Enter | To verify, enter the command as shown to get the list of images.
We can see that the tagged image is no longer in the list. |
| Type sudo docker pull stuser1/node-express and press Enter | Now let us pull the image from Docker Hub.
For that, type the command as shown and press Enter. |
| Highlight the output | We can see that the image is successfully pulled and downloaded. |
| Only narration | Now let us move forward to image layers and size optimization. |
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Image Layers and Size Optimization |
Docker images are built in layers.
Each Dockerfile instruction that changes the filesystem, represents a layer. To optimize image size, the number of layers are reduced. |
| Only narration | Nowl et us see how this actually works. |
| Type sudo docker images grep node-express and press Enter | Switch to the terminal.
First, we will check the size of our image. Type the command as shown. |
| Highlight grep node-express | I have extended the command with pipe spacegrep space image name.
We don’t need to specifyany version or tag of the image. It filters the image list and retrieves details for the specified image name only. |
| Press Enter | Press Enter. |
| Highlight the output | We can see that the size of our imageis 1.13GB.
This size may be different for you. |
| Type cd ~/Downloads and press Enter | Make sure you are in the directory where you have downloaded the code files. |
| Type sudo nano Dockerfile and press Enter | Let us go to Dockerfile, using the nano Dockerfile command.
Enter the password when prompted. |
| Only narration | In this file, there area total of six instructions.
However, WORKDIR and CMD do not create new filesystem layers. Thus , the Docker image will have four layers from the Dockerfile instructions. |
| Highlight node:latest | Here the latest version of the node base image is used.
To reduce the size, we can use a smaller base image. |
| Replace node:latest with node:slim | Replace the word latest and type slim.
Then save by pressing Ctrl+S and exit by pressing Ctrl+X. |
| In terminal, type sudo docker build -t node-express:v1 . and press Enter | Again build the image.
Type the command as shown and press Enter. |
| Highlight the output | The image is built successfully. |
| Type sudo docker images grep node-express and press Enter | Nowlet us check the size of the image.
Enter the commandas shown. |
| Highlight the output | We can see that now our image size is reduced to 232MB.
This size may be different for you. |
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Summary |
This brings us to the end of this tutorial. Let us summarize.
In this tutorial, we have learnt about
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Assignment |
As an assignment, please do the following:
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Assignment Observation |
The size of the imageis optimized to 160MB.
This size may be different for you. |
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About Spoken Tutorial project |
The video at the following link summarizes the Spoken Tutorial project.
Please download and watch it. |
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Spoken Tutorial Workshops |
The Spoken Tutorial Project teamconducts workshops and gives certificates.
For more details,please write to us. |
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Answers for THIS Spoken Tutorial |
Please post your timed queries in this forum. |
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FOSSEE Forum |
For any generalor technical questions on docker, visit the FOSSEE forumand post your question. |
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Acknowledgement |
Spoken Tutorial Project was established by the Ministry of Education, Government of India. |
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Thankyou
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This is Pranjal Mahajan, a FOSSEE Semester Long Intern 2024, IIT Bombay signing off
Thanks for joining. |
